This project will examine the activation of chemical procarcinogens by mammary gland cells. A mammary cell mediated mammalian cell mutagenesis assay will be employed. In this assay, primary mammary cells are co-cultivated with an established cell line, V79, that cannot activate carcinogens. The co-cultures are exposed to the procarcinogen after which the V-79 cells are separated from the mammary cells and tested for the induction of two specific locus mutations. Employing this system, we will examine the specificity of carcinogen activation by mammary cells and the effects of physiological and non-physiological agents on this process. In addition, we will compare rat strains of differing susceptibility to chemically induced mammary cancer for ability of their mammary cells to activate procarcinogens. The relative abilities of various mammary cell types to activate carcinogens will also be studied. Complimentary biochemical and biological studies will be performed. Initially, rat mammary cells will be used, and later, the assay will be extended to study human cells.